SAN FRANCISCO - A defendant may avoid execution if he is mentally deficient, even if his IQ score is in the normal range, California's highest court has ruled.

The California Supreme Court issued a unanimous ruling Thursday, overturning a lower court decision that composites of tests measuring various mental faculties -- also known as "full scale" IQ scores -- are the best measure of intelligence, The Los Angeles Times reported.

The court found that courts may give greater weight to one measurement of IQ over another, and that the best measure of intellectual functioning may vary from one case to another, the newspaper said.

The decision clarifies a 2005 ruling that allowed California deathrow inmates to challenge their death sentences on the basis of mental retardation. The U.S. Supreme Court issued a ruling in 2002 that barred execution of the mentally retarded.

John Philipsborn, a lawyer for an association of criminal defense lawyers in the case, told the Times the ruling will affect at least 28 deathrow inmates and at least eight defendants who are awaiting trial and claiming mental retardation.